1. Field of the Invention
The present invention relates to a particle counter having an adjustable probe, and more particularly, to a particle counter having an adjustable probe that is capable of reducing particle count measurement errors by varying the intake area of a sampling probe according to the speed of the air within a clean room to be measured.
2. Discussion of the Related Art
Present manufacturing processes and methods require ultra-precision, high-purity, and contamination free environments. Technology related to cleaning and reducing contaminants in the manufacturing process substantially improves the performance and the production yield of many present day products.
Clean rooms, in particular, have been used widely in many industries, including: the electronics industry for such products as semiconductors and liquid crystal displays; the precision instrument field; the chemical field, especially when manufacturing chemicals for semiconductor devices where chemical purity is important; and hospitals, medical supply factories, and the food industry where microbe pollution becomes an issue.
In particular, clean rooms in the semiconductor industry seek to control the amount of particles floating in the air so that the particles do not reach and contaminate the working object in the space. In the clean room, the temperature, humidity, interior pressure, illumination, noise and vibration, etc. are controlled and managed simultaneously. Clean room management is based on relative degrees or classes of cleanliness, as determined by the concentration and diameter of particles existing in the space.
Various measurement apparatuses have been developed to facilitate clean room management. One such measurement apparatus, a condensation particle counter, operates under the principle that the particle size increases during an alcohol evaporation process. Another measurement apparatus, an optical particle counter, measures the intensity of light scattered by the particles after projecting a laser into the sampled air containing the particles.
FIG. 1 is a perspective view showing a conventional optical particle counter. In the particle counter 10, a counter body 12 and a sampling probe 20, for sampling the air containing particles, are connected via a sampling tube 18. Formed in the counter body 12 are a display section 14, which is capable of displaying a measurement result, and an adjusting section 16, which is capable of adjusting a switch or setting a value. Also, a pump (not shown) is operated to suction the air to be measured through the sampling probe 20. A laser tube (not shown) projects the laser light into the sampling air to be measured, and a photo detector (not shown) detects the scattered laser light caused by collisions between the projected laser light and particles.
FIG. 2 is a perspective view showing the conventional sampling probe 20 of FIG. 1 in greater detail. A handle 22 is provided at the connection point between the funnel-shaped sampling probe 20 and the sampling tube 18 so that an operator can hold it while taking particle measurements. The interior wall 21 of the sampling probe 20 is flat.
In operation, a technician orients the sampling probe 20 toward a specific flow direction of the air to be measured in order to sample the air. It is preferable that the air speed as suctioned by the pump through the intake 23 of the sampling probe 20 should coincide with the air speed of the atmosphere in close proximity to the probe 20. When the air speed of the atmosphere to be measured does not coincide with the air speed at the intake 23 of the probe 20, measurement errors occur. As a result, the cleanliness management of the clean room is less than optimal.
FIGS. 3A, 3B and 3C illustrate various air flows that result according to the relationship between an interior air speed (hereinafter referred to as `probe air speed`) at the intake 23 of the probe 20 and the atmospheric air speed in close proximity to the probe 20.
FIG. 3A depicts the situation where the atmospheric air speed is greater than the probe air speed, FIG. 3B depicts the situation where the atmospheric air speed is less than the probe air speed, and FIG. 3C depicts the situation where the atmospheric air speed is equal to the probe air speed.
As shown by the arrows in FIG. 3A, when the atmospheric air speed, as generated by a clean air circulating pump (not shown) for the clean room system, is greater than the probe air speed generated by a sample suction pump within the air particle counter 10, outward eddy flows 26 are generated near the edges of the intake area 23 of the probe 20. The lower pump suction pressure causes particles that would normally have been suctioned into the probe 20 to be scattered away from the probe 20 by the outward flowing eddies 26. Accordingly, the number of particles entering the probe 20 and measured by the particle counter 10 are decreased, resulting in measurement errors and decreased reliability in the management of the clean room.
As shown by the arrows in FIG. 3B, when the atmospheric air speed, as generated by a clean air circulating pump (not shown) for the clean room system, is less than the probe air speed generated by a sample suction pump within the air particle counter 10, inward eddy flows 26 are generated near the edges of the intake area 23 of the probe 20. However, in this case, the higher pump suction pressure causes particles that would normally not have been suctioned into the probe 20 to be suctioned into the probe 20. Accordingly, the number of particles entering the probe 20 and measured by the particle counter 10 are increased, resulting in measurement errors and decreased reliability in the management of the clean room.
The preferred or optimum case would be as shown in FIG. 3C where the atmospheric air speed is equal to the probe air speed, whereby the correct amount of particles enter the probe 20, thereby minimizing measurement errors.
Present air particle counter probes have intakes that are manufactured to a general specification based on an average air speed of a typical clean room. For example, an air particle counter may be designed to sample the air at a speed of 1 cubic foot per minute according to an international standard. Accordingly, for a probe having an intake diameter of 3 cm, the probe air speed should be 0.667 m/sec for optimum results.
However, the air speeds in clean rooms for a semiconductor production are different, ranging from 0.1 m/sec to 0.7 m/sec, for example. A problem thus exists since the precise number of particles cannot be measured with the conventional fixed intake sampling probe, except for the one condition where the atmospheric air speed precisely matches the probe air speed. Since the various types of clean rooms in other industries also have different air speeds according to the type and function of the clean room, the above problem is continuously evident throughout the art.